There is provision for airbridges within the masterplan. The architect's plan on page 99 clearly shows 3. The two-storey pier would be a larger version of the current bus shelter running the length of the extended terminal before turning and extending out into the main apron (I assume at the point where the current fire station is). In the plan there are three larger stands where the pier extends out onto the apron which I assume would hold a 757/767/787. The reason for the refusal of airbridges during the original construction of the terminal was that the building would have to be raised higher and have a proper second floor airside and this would (in the planners view) have disturbed the sightlines of the surrounding countryside because the building would be too intrusive. I would have thought in the current climate airbridges could be shown to be environmentally friendly. It would reduce the number of bus movements per year (to the current 767 stand)! If the airport is to attract full service airlines especially a Middle Eastern airline it needs to offer full service facilities such as airbridges. It is embarrassing when returning to Bristol with Continental to hear the cabin crew announce in very surprised and mystified tones that Bristol is an airport without airbridges and the pax will be disembarking by those quaint things called steps!
The state of the terminal is only going to get worse before it gets better. Heathrow is a prime example of what goes wrong when you have too much traffic going through inadequate facilities. The airport is run by private enterprise and they will want to wring every last penny out of the existing building. Airports that are a joy to use because they have space to breathe don't make half as much money as one where you are maximising the facilities and some!